Saline is a solution that contains a certain amount of NaCl and is designed to have the same osmotic pressure as normal blood cells. Doctors often give saline to patients who have lost blood. Which of the following explains why glucose of the same molality cannot attain the same effect as saline?
Each formula unit of NaCl will give two particles because of ionization, but each molecule of glucose dissolves to give only one particle. Osmotic pressure for glucose will be lower than is required.
Glucose would not maintain osmotic pressure because on dissociation it forms two particles per formula unit, but NaCl would give only one particle per formula unit. Osmotic pressure is higher when the number of particles decreases.
Osmotic pressure increases with the decrease in the number of particles of solute in the solution. NaCl provides fewer particles per formula unit than glucose does.
Sodium and chloride ions can pass freely through the membranes of red blood cells, but glucose molecules cannot pass through the membranes.
Osmotic pressure, P is given by
P = i*C*R*T
where i is the number of particles formed after dissociation in solution
Glucose being covalent compound doesn't dissociate but NaCl dissociate as it is ionic
NaCl ---> Na+ + Cl-
So i=1 for glucose but its 2 for NaCl
Answer is:
Each formula unit of NaCl will give two particles because of ionization, but each molecule of glucose dissolves to give only one particle. Osmotic pressure for glucose will be lower than is required.